Cellular receptors for rabies virus, a strictly neurotropic pathogen in vivo will be studied in vitro with cells of neural and non-neural origin. the specificity of the host cell receptor for rabies virus will be compared to that for neurovirulent and avirulent rabies strains and eventually to viruses with related neurotropisms. Direct evidence that the rabies virion"spike" glycoprotein is responsible for the attachment of virions to a complementary cellular receptor unit (CRU) will be obtained from competitive attachment inhibition experiments. The minimum essential structure of the virion attachment protein (VAP) required for attachment to the CRU will be investigated using a large size aggregate of purified native "spikes" and smaller forms of the VAP down to glycopeptide fragments of the virion "spike" glycoprotein. The attachment site on the VAP and its conformational structure will be investigated separately with monoclonal antibodies directly against the VAP and with chemically modified VAP preparations as blocking reagents to inhibit VAP attachment to CRUs. Inhibition of virion attachment to susceptible cells which is caused by monoclonal antibodies directly against cell surface antigens of mouse neuroblastoma cells (anti-"receptor" activity) will be further investigated with anti-"receptor" monoclonal antibodies to evaluate the presence of cell surfacr receptor antigen(s) on uninfected and rabies virus-infected cells. Anti-"receptor" monoclonal antibodies presently available and those which will be produced with soluble receptor components as immunogen will provide powerful tools with which to search for comparable specific receptor activity in vivo. Finally, soluble VAP-CRU attachment complexes will be isolated from cells to analyze the radiolabeled receptor components involved in the binding of virus beginning with the initial attachment stage and ending with viropexis.